1. Field of the Invention
The present invention relates to a bearing structure that rotatably supports a roller and a fusing device for an image forming apparatus employing the bearing structure. More particularly, the present invention relates to a bearing structure that reduces friction between a roller and a bearing under pressure and a fusing device for an image forming apparatus employing the bearing structure.
2. Description of the Related Art
In general, bearing structures are employed to rotatably support a roller on a fixed frame. That is, bearing structures are installed at both sides of a roller to be connected between the roller and the frame, and to rotatably support the roller.
Bearing structures are divided into a ball bearing type, which rotatably supports a roller by balls that roll between an inner wheel and an outer wheel, and a sliding bearing type, which is made of plastic material and rotatably supports a roller by allowing the roller to slide. The ball bearing is superior in performance to the sliding bearing, but has a complex structure, thereby increasing the number of assembling processes and manufacturing costs. Accordingly, the sliding bearing, which can be mass produced easily at low costs, is widely used.
In general, electrophotographic image forming apparatuses print an image on a sheet of paper by emitting light to a photosensitive medium charged at a predetermined potential to form an electrostatic latent image, developing the electrostatic latent image with toner of a predetermined color to form a toner image, and transferring and fusing the toner image. The image forming apparatuses employ a fusing device in a printing path to fuse the transferred image on the sheet of paper.
Referring to FIGS. 1 and 2, a conventional image forming apparatus includes a frame 1, a fusing roller 11 installed for being rotatable on a frame 1, a heater 15 embedded in the fusing roller 11 for heating a surface of the fusing roller 11, a pressure roller 21 rotatably installed on the frame 1 for pressing a printing paper P with the fusing roller 11, and bearing structures 30 for rotatably supporting the fusing roller 11 and the pressure roller 21.
Each of the bearing structures 30 includes a sliding bearing 31 installed on the frame 1, and an elastic member 35 for supporting elastically the sliding bearing 31. The sliding bearing 31 is made of plastic material, and has a bearing groove 33 into which the fusing roller 11 or the pressure roller 21 is rotatably inserted. Here, a clearance is formed between an inner surface of the bearing groove 33 and an outer surface of each of the fusing roller 11 and the pressure roller 21. A fluid is injected into the clearance, and guides the fusing roller 11 and the pressure roller 21, thereby helping them to slide during their rotation. The elastic member 35 elastically supports the sliding bearing 31 in a predetermined direction, and the pressure roller 21 presses the fusing roller 11.
In this manner, if the fusing roller 11 and the pressure roller 21 are rotatably supported while pressure is applied therebetween in a predetermined direction, a predetermined area on the inner surface of the bearing groove 33, that is, an area A formed in a direction opposite to the direction in which the pressure is applied, has a narrower clearance than other areas, such that the area A directly contacts the fusing roller 11 or the pressure roller 21 with a higher load.
With the increase in the load, the sliding bearing 31 may be worn, and the system may operate wrongly or halt. Further, foreign substances C generated during the wear may remain inside the bearing groove 33, thereby causing the bearing to operate abnormally.
In the meantime, it can be considered that the fusing device can employ a ball bearing. However, since the ball bearing is large and a mold bearing should be used inside the ball bearing, the ball bearing has a complex structure and increases the number of assembling processes and manufacturing costs as compared to the sliding bearing.
Further, since the ball bearing is made of metal material stronger than the plastic material of the sliding bearing, even when the fusing roller is heated by the heater installed thereinside to an abnormally high temperature where plastic material may be deformed, the ball bearing is not deformed. In the meanwhile, a general fusing device employs a fuse, which determines whether the bearing is overheated based on the degree of deformation of the heated bearing and stops the heating if it is determined to be overheated. Accordingly, if the fusing device constructed as above employs the ball bearing, the bearing is not deformed at an abnormally high temperature, thereby increasing the possibility of fires. Thus, the fusing device employing the fuse cannot be used.